This invention reslates to acoustic distance measuring devices in general, and in particular to a novel type of ultrasonic distance measuring apparatus employing self-oscillation in alternate half-wavelengths of feedback path length.
Several types of acoustic distance measuring devices are in use, the most common being variations of the pulse-echo system, which bounces ultrasonic pulses from a surface and uses a timing circuit to measure the elapsed time between the pulse transmission and the return of the echo. By knowing the velocity of sound and the travel time, the distance to the reflecting surface can be determined. Some devices include complex reference system to compensate for changes in the velocity of sound or variations in the timing circuit.
Pulse-echo systems are limited in their ability to sense small changes in distance, as the accuracy of the timing circuit is limited. These systems tend to be relatively complex and expensive.